CVE-2017-7539 in QEMU
Summary
by MITRE
An assertion-failure flaw was found in Qemu before 2.10.1, in the Network Block Device (NBD) server's initial connection negotiation, where the I/O coroutine was undefined. This could crash the qemu-nbd server if a client sent unexpected data during connection negotiation. A remote user or process could use this flaw to crash the qemu-nbd server resulting in denial of service.
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Analysis
by VulDB Data Team • 04/25/2023
The vulnerability identified as CVE-2017-7539 represents a critical assertion failure within the QEMU virtualization platform's Network Block Device (NBD) server implementation. This flaw exists in QEMU versions prior to 2.10.1 and specifically affects the initial connection negotiation phase where the I/O coroutine remains undefined. The issue stems from insufficient input validation and error handling during the NBD server's connection establishment process, creating a scenario where malformed or unexpected client data can trigger an assertion failure that results in immediate server termination.
The technical exploitation of this vulnerability occurs when a remote attacker or local process sends unexpected data packets to the qemu-nbd server during the connection negotiation phase. The NBD server, which operates as a network service providing block-level access to virtual machine storage, fails to properly validate incoming connection parameters. When the server encounters malformed data structures or unexpected protocol sequences during the initial handshake, the undefined I/O coroutine state causes the assertion to fail and subsequently crashes the entire server process. This assertion failure represents a classic example of improper error handling and lack of input sanitization within network services.
From an operational perspective, this vulnerability creates a significant denial of service risk for systems relying on QEMU's NBD server functionality. The crash occurs during the connection negotiation phase, meaning that legitimate clients attempting to establish connections may be interrupted by the service crash, while malicious actors can reliably trigger the denial of service condition. The impact extends beyond simple service disruption as it affects virtualized environments where NBD servers are used for storage provisioning, backup operations, and live migration scenarios. Organizations running QEMU-based virtualization platforms with exposed NBD servers face potential operational downtime and service unavailability.
The vulnerability maps directly to CWE-617: "Reachable Assertion" which describes situations where assertions can be triggered by external input, and aligns with ATT&CK technique T1499.004: "Endpoint Denial of Service" in the context of virtualization platforms. The flaw demonstrates poor defensive programming practices where the system fails to handle unexpected input gracefully, instead allowing the program to terminate abruptly. This vulnerability also reflects broader concerns in virtualization security where network services exposed to untrusted networks require robust input validation and error handling mechanisms. Organizations should implement immediate patching of QEMU installations to version 2.10.1 or later, while also considering network segmentation and access controls to limit exposure of NBD services to trusted networks only. Additional mitigations include implementing monitoring for unusual connection patterns and ensuring that virtualization platforms are properly configured with appropriate security boundaries to prevent unauthorized access to NBD server functionality.